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Chip brings e-paper display to interactive apps

Posted: 21 Apr 2008 ?? ?Print Version ?Bookmark and Share

Keywords:e-paper displays? e-paper display controller? active-matrix electrophoretic displays?

Electrophoretic "electronic paper" displays will get a speed boost next month as a result of a deal between E Ink Corp. and Seiko Epson Corp. The companies have jointly developed an electronic-paper display controller that they claim breaks the speed bottleneck that has stood in the way of e-paper's use for interactive applications.

"Many OEMs thought that active-matrix electrophoretic displays were too slow for stylus input or drop-down menusor even to keep up with a fast typistbut the bottleneck was the controller chip," said Sri Peruvemba, VP of marketing at E Ink. "The engineers at Epson helped us design a controller chip that proves interactive applications are possible for electrophoretic displays."

Displays get smarter
The main advantage of such displays is that they use reflected light instead of a backlight, making them easy to read at any angle in normal room lighting as well as in bright sunlight. LCDs, by contrast, are hard to read in sunlight and have a limited viewing angle.

With the faster Epson-manufactured controller, E Ink claims that electrophoretic displays can tackle nearly every application now served by LCDs, albeit only in black and white (or a limited number of gray scales). Applications include e-books, newspapers, -notebooks and -dictionaries; tablet PCs; and auxilliary displays for ordinary laptop computers.

How it works
Electrophoretic displays work by trapping microcapsules of white and black pigmentelectronic inkinside a thin film, where they float in a transparent liquid. The black microcapsules are negatively charged and the white ones positively charged. By laminating the film onto a substrate that can apply an electrical charge, either the black or the white microcapsules of electronic ink can be forced to the surface at specific pixel locations. Both rigid and flexible substrates, ranging in pixel density from 100 to 400dpi, have been demonstrated with E Ink's electrophoretic displays.

Unlike an LCD, which must refresh each pixel location about every 15ms, electrophoretic displays do not require a raster scan of the entire display. Rather, the controller only sends an electrical signal to the pixels that need to be changed. Consequently, the controller that supplies the electrical charge to the substrate can operate on a slower time scale, of about 250ms per pixel change. The new, speedier controller chip jointly developed by E Ink and Seiko Epson can change the state of up to 16pixels simultaneously, increasing the perceived speed of the display to be on a par with that of LCDs (about 15ms).

High performance controller
E Ink's previous display controller did not perform parallel pixel updates, making devices noticeably sluggish, especially when changing the state of an entire page. E Ink claims the new chip enables interactive user interfaces to be designed for e-ink displays supporting real-time keyboard entry, stylus-based sketching, and navigational menus and cursors.

"We got the fastest typists we could find in our company to try it out, and none of them could type faster than the new controller," said Peruvemba. "We have also tried displaying video and have gotten a response that looks like an LCD, when in fact it is still using the same electrophoretic technology as before."

E Ink claims dozens of OEMs are readying devices, using both rigid and flexible substrates, based on its electrophoretic displays. The most notable designs to date include e-books from Sony and, but six other OEMs have been announced, including Samsung and LG Electronics. Epson itself is readying devices using E Ink's electrophoretic displays.

The new controller chips (Epson part number S1D13521B) will be made available to OEMs next month. Also available will be a reference design module, called the AM300 Broadsheet, that will include a complete electrophoretic display measuring 5- to 9.7-inches on the diagonal, along with the Epson-manufactured display controller, other necessary drive circuitry and a compact flash card slot to hold the images to be displayed.

- R. Colin Johnson
EE Times

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